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_Sleep is generally defined as a period during which the body and mind are at rest, as if disconnected from the world. © Nicolas Decat_ WHEN WE SLEEP WE ARE NOT COMPLETELY CUT OFF FROM OUR

ENVIRONMENT: WE ARE STILL ABLE TO HEAR AND UNDERSTAND WORDS. THESE OBSERVATIONS, RESULTING FROM THE CLOSE COLLABORATION BETWEEN RESEARCHERS FROM INSERM, CNRS, SORBONNE UNIVERSITÉ AND AP-HP

AT THE BRAIN INSTITUTE AND THE DEPARTMENT OF SLEEP DISORDERS AT PITIÉ-SALPÊTRIÈRE HOSPITAL IN PARIS, CALL INTO QUESTION THE VERY DEFINITION OF SLEEP AND THE CLINICAL CRITERIA THAT

DISTINGUISH BETWEEN ITS DIFFERENT STAGES. THEY ARE DETAILED IN A NEW STUDY PUBLISHED IN _NATURE NEUROSCIENCE_. Sleep is generally defined as a period during which the body and mind are

resting, as if disconnected from the world. However, a new study led by Delphine Oudiette, Inserm researcher, Isabelle Arnulf (Sorbonne Université, AP-HP) and Lionel Naccache (Sorbonne

Université, AP-HP) at the Brain Institute, shows that the boundary between wakefulness and sleep is much more porous than it would appear. The scientists have shown that sleepers with no

particular disorders are able to capture verbal information transmitted by a human voice and respond to it by contracting facial muscles. What is more, this astonishing ability manifests

itself intermittently during almost all stages of sleep — as if windows to the outside world were temporarily opened. These new data on sleep behavior suggest that it may eventually be

possible to develop standardized protocols for communication with sleepers in order to better understand how mental activity changes during sleep. On the horizon: a new access route to the

cognitive processes that underpin normal and pathological sleep. A THOUSAND AND ONE VARIATIONS IN CONSCIOUSNESS > “_Even if it seems familiar to us because we do it every night, > 

sleep is a very complex phenomenon. Our research has taught us that > wakefulness and sleep are not stable states: both resemble a > kaleidoscope of conscious moments… and moments that

 do not appear > to be so,”_ explains Prof. Lionel Naccache, neurologist at > Pitié-Salpêtrière Hospital AP-HP and neuroscience researcher. It is essential to improve our understanding

of the brain mechanisms that underlie these intermediate states between wakefulness and sleep. > “_When out of sync, they can be associated with disorders such as > sleepwalking, 

sleep paralysis, hallucinations, the feeling of not > sleeping at night or, on the contrary, sleeping with the eyes > open_“, explains Prof. Isabelle Arnulf, head of the Sleep > 

Disorders Department at Pitié-Salpêtrière Hospital AP-HP. However, in order to distinguish between wakefulness and the different stages of sleep, we have so far used simple and inaccurate

physiological indicators, such as specific brain waves made visible through electroencephalography. Such indicators do not capture in detail what is going on inside the heads of sleepers,

especially as they are sometimes in contradiction with what the sleepers tell us themselves. > “_We need more refined physiological measurements that are aligned > with the sleeper’s 

feelings and ability to respond to the outside > world__; this is to better define their level of vigilance_“, adds > Delphine Oudiette, Inserm researcher in cognitive neuroscience. A

GAME BETWEEN UNCONSCIOUSNESS AND LUCIDITY The research team[1] therefore explored this avenue and recruited 22 people without sleep disorders and 27 narcoleptic patients — i.e. victims of

irrepressible sleep episodes. People with narcolepsy have the particularity of having many lucid dreams, namely in which they are aware of being asleep and can sometimes shape the scenario.

In addition, they easily and quickly reach REM sleep (the stage where the lucid dream emerges) during the day, making them good candidates for studying consciousness during sleep under

experimental conditions. > “_One of our previous studies__ had shown that two-way > communication, between the scientist and the dreamer and vice versa, > is possible during lucid 

REM sleep_, explains Oudiette. _For our > latest study,__ we wanted to know if these findings could be > extrapolated to other sleep stages and to individuals who do not > have 

lucid dreams_. “ The study participants were asked to take a nap. The researchers had them do a “lexical decision” test in which a human voice uttered a series of words, both real and made

up. The participants had to respond by smiling or frowning, in order to place the words in one of the two categories. Throughout the experiment, the participants were monitored using

polysomnography—a comprehensive examination to record their brain and heart activity, eye movements, and muscle tone. Finally, upon waking, they had to report whether or not they had a lucid

dream during their nap, and whether they remembered interacting with someone. > “_Most of the participants, whether narcoleptic or not, managed to > respond correctly to the verbal 

stimuli while sleeping. These events > were admittedly more frequent during episodes of lucid dreams, > characterized by a high level of consciousness; however, we observed > them 

occasionally in both groups, during all sleep phases”_, > specifies Arnulf. By combining these physiological and behavioral data with the subjective reports of the participants, the

researchers also show that it is possible to predict the opening of these windows of connection with the environment, i.e. the times when the sleepers were able to respond to stimuli. These

were heralded by an acceleration of brain activity, and by physiological indicators usually associated with rich cognitive activity. > “_In people who had a lucid dream during their nap, 

the ability to > dialog with the investigator and talk about this experience on > waking was also characterized by a specific electrophysiological > signature_, adds Naccache. _Our 

data suggest that lucid dreamers > have privileged access to their inner world, and that this increased > awareness also extends to the outside world. _“ Further research will be

needed to determine whether the increase in these windows is correlated with sleep quality, and whether they could be used to improve certain sleep disorders or promote learning. > “_More

 advanced neuroimaging techniques, such as > magnetoencephalography and intracranial recording of brain activity, > will help us to better understand_ _the brain mechanisms that > 

orchestrate sleep behaviors_“, concludes Oudiette. Finally, these new data could help to revise the definition of sleep, a state that is ultimately very active, perhaps more conscious than

we thought, and open to the world and others. _This study was funded by the French National Research Agency and the French Society for Sleep Research and Medicine (SFRMS)._ [1] Including PhD

students Başak Türker, Esteban Munoz Musat and Emma Chabani, whose participation was essential to the conduct of this study.  THESE CONTENTS COULD BE INTERESTING :